The present invention is related to vacuum support systems. More particularly it relates to a self adaptive vacuum support system, employing aerodynamic forces.
Vacuum support systems are widely used in many industrial areas. A vacuum support system may serve either to fix an object in place or to hold an object while it is being conveyed from one location to another. Vacuum support systems are widely in used in the Hi-Tech Industries. Holding a wafer during its fabrication process or during deicing in the Semiconductors (SC) industry, holding a Printed Circuit Board (PCR) or a flat-screen during Automatic Optical Inspection (the AOI industry), or holding an aluminum printing-plate to a rotating drum in the Printing or Art-Graphic industries, make just a short list of examples where vacuum support systems are being utilized.
Vacuum support systems employ the pressure difference between a higher ambient pressure that acts on the object upper surface, and the vacuum imposed on the object lower surface. The pressure difference, multiplied by the effective area, makes up the force that holds the object (hereafter referred to as xe2x80x9cvacuum-forcexe2x80x9d). In Conventional systems, the vacuum-force is linearly dependent on both the pressure difference and the effective area.
Conventional vacuum-support systems comprise a vacuum pump fluidically connected by vacuum-pipes to a plurality of drilled cylindrical holes arranged on the system contact surface. In most cases, the contact surface is flat or a cylinder. In many practical cases such simple solution is not acceptable. A common vacuum support system failure occurs when a plurality of vacuum-conduits (i.e. the holes) are present but a significant number of them are not covered because the object to be held is smaller than the vacuum-frame. Another common problem in such systems may occur, when the object is not fully attached to the contact surface, or when the surface of the object has cavities and/or grooves, allowing air to escape through and failing to obtain a substantial vacuum force. In addition, situations where some of the initially closed vacuum-conduits become exposed during the process (such as the dicing process), are very common in the SC industry.
When all the vacuum-conduits are blocked, the parasite mass flow rate (hereafter referred to as MFR), of the air through the conduits is accountable and acceptable, but when a significant number of vacuum-conduits are opened, the parasite MFR severely increases, the vacuum level may critically degrade, and the vacuum-force may be lost. Many improvised solutions had been suggested to reduce the occurrence of parasite MFR: covering the exposed vacuum-conduits before operation, or activating only sectors of the vacuum-frame to introduce the vacuum only to the xe2x80x9cactivexe2x80x9d section of the vacuum-frame, are some of such solutions. However these are only partial semi-effective solutions.
The problem of parasite MFR must be solved in order to achieve reliable vacuum support system. One common way, is to use a powerful vacuum pump to provide the required vacuum level to account for the presence of parasite MFR. Such a solution is expensive (the cost of powerful pump and auxiliary equipment and the wasted energy when the system operates), and occupies unnecessary volume and weight. It may also be a powerful source for significant noise and mechanical vibrations. In particular, the use of a simple vacuum-conduit may result in an unacceptable noise. Simple vacuum-conduits can not sustain internal pressure drops, and, therefore, when the vacuum-conduits are open and subjected to external pressure gap, the mechanism of external pressure relaxation (at the vacuum-conduits exit), may involve noisy jets. In cases where the external pressure gap is sufficiently large, super-sonic (extremely noisy) jets may develop. In such noisy situations the use of vacuum support systems may be questionable, when xe2x80x9cquiet roomxe2x80x9d conditions are required.
Other solutions exist where small diameter vacuum-conduits are used, ending with enlarged effective area, thus MFR is reduced and the required vacuum-force is obtained. Such brute-force solutions severely increase the risk of mechanical blockage by contaminants, being particles or liquid. However, such mechanical blockage results in a loss of the vacuum-force, and it may dramatically increase maintenance expenses. In addition, small diameter vacuum-conduits are characterized by poor time response, including the response to control commands.
Solutions to control the MFR based on using an individual valve-like control device for each of the vacuum-conduit, are not practical, especially when a large number of vacuum-conduits are used. Valves are more expensive, and may involve mechanical or electromechanical means, thus the maintenance task becomes unfeasible. Controlling the parasite MFR must be solved in a favorable way, to meet the practical requirements for a well-functioning vacuum support system.
The Self Adaptive Vacuum Support Apparatus disclosed in the present Invention is based on the SASO concept, as described in detail in our Israeli Patent Application titled SELF ADAPTIVE SEGMENTED ORIFICE (SASO) DEVICE AND METHOD, simultaneously filed with the present application.
The only related prior art references having some relevance to the present invention deal with irrigation emitters only where the fluid passing through it is water which is practically incompressible (as opposed to air or other gases).
U.S. Pat. No. 3,896,999 (Barragan) disclosed an anti-clogging drip irrigation valve, comprising a wide conduit equipped with a plurality of partition means, integrally formed with the conduit wall, forming labyrinth conduits, in order to reduce the water pressure prior to its exit through the labyrinth conduits outlet.
U.S. Pat. No. 4,573,640 (Mehoudar) disclosed an irrigation emitter unit providing a labyrinth conduit similarly to the valve in U.S. Pat. No. 3,896,999. Examples of other devices providing labyrinth conduits for the purpose of providing a pressure drop along the conduit can be found in U.S. Pat. No. 4,060,200 (Mehoudar), U.S. Pat. No. 4,413,787 (Gilead et al.). U.S. Pat. No. 3,870,236 (Sahagun-Barragan), U.S. Pat. No. 4,880,167 (Langa), U.S. Pat. No. 5,620,143 (Delmer et al.), U.S. Pat. No. 4,430,020 (Robbins), U.S. Pat. No. 4,209,133 (Mehoudar), U.S. Pat. No. 4,718,608 (Mehoudar), U.S. Pat. No. 5,207,386 (Mehoudar).
In a labyrinth conduit the aerodynamic resistance is substantially large due to the viscous friction exerted by the walls of the conduit (acting opposite to the direction of the flow), and as the passage becomes tortuous and lengthier (that""s the essential feature of a labyrinth) more wall contact surface is acting on the flow, increasing the viscous friction. In some cases cavities are provided for intercepting contaminants and for freeing the flow passage. None of these patents, which basically deal with two dimensional geometry (the third being either very small or degenerated), mention or make use of a vortical aerodynamic blockage mechanism, that is an essential feature of the present invention.
It is emphasized that while the above mentioned patents deal with the delivery of water through the conduit, the present invention seeks to provide and exploit aerodynamically induced vacuum grip force, with the fluidxe2x80x94air in most casesxe2x80x94merely serving as the means for generating this force, and on the other hand reducing the parasite mass flow rate through the conduit when the vacuum grip at the conduit""s inlet is lost.
In an article titled xe2x80x9cA FLOW VISUALIZATION STUDY OF THE FLOW IN A 2D ARRAY OF FINSxe2x80x9d (S. Brokman, D Levin, Experiments in Fluids 14, 241-245 (1993)) a study of the flow field in a 2D arrangement of fins was carried out by means of flow visualization in a vertical flow tunnel. The study was related to an earlier studies that examined the fin arrangement as a conceptual heat sink. The above mentioned study went further to examine the complex flow field structure in order to obtain a better understanding of the heat convection process. A model was built of several series of fins, simulating a spatially unlimited multi-cell structure. Two main flow structures were observedxe2x80x94a flow separation from the leading edge of each fin, which due to the influence of neighboring fins, was reattached to the fin, creating a closed separation zone, and a vortex, that filled that closed separation zone.
It is therefore provided, in accordance with a preferred embodiment of the present invention, a self-adaptive vacuum grip apparatus comprising: a vacuum source; a vacuum reservoir fluidically connected to said vacuum source; a contact surface; at least one conduit of a plurality of conduits; wherein said conduit has an inlet positioned on said contact surface and an outlet fluidically connected to said vacuum reservoir said conduit is provided with a plurality of fins mounted on the internal wall of said conduit said fins arranged in two arrays substantially opposite each other; wherein each of the fins of either one of said fin arrays excluding the fin nearest to the inlet and the fin nearest to the outlet of said conduit is positioned substantially opposite one of a plurality of cavities each cavity defined between two consecutive fins of one of said arrays of fins and a portion of said conduit internal walls wherein said two opposing fin arrays are arranged asymmetrically; whereby when fluid flows through said conduit a plurality of vortices formed within said cavities said vortices existing at least temporarily during said flow thus forming an aerodynamic blockage allowing a central core-flow between said vortices and the tips of said fins suppressing the flow in a one-dimensional manner thus limiting the mass flow rate and maintaining a substantial pressure drop within the conduit; and whereby when an object blocks the inlet of said conduit the flow stops said vortices dissipate thus said object is effectively held by the vacuum induced force to said contact surface whereas when the inlet is not blocked said vortices are formed and aerodynamically block the flow through said conduit and when said conduit inlet is not blocked by said object the required vacuum level of said vacuum reservoir is maintained with significantly reduced power consumption supplied to generate the required vacuum condition.
Furthermore, in accordance with a preferred embodiment of the present invention, said fluid is air.
Furthermore, in accordance with a preferred embodiment of the present invention, said fins are L-shaped where the thin core-flow is suppressed in a two-dimensional manner by said vortices.
Furthermore, in accordance with a preferred embodiment of the present invention, said fins are U-shaped where the thin core-flow is suppressed in a two-dimensional manner by said vortices.
Furthermore, in accordance with a preferred embodiment of the present invention, conduit follows a straight path.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit follows a tortuous path.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit cross-section is substantially rectangular.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit cross-section is substantially polygonal.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit cross-section is substantially circular.
Furthermore, in accordance with a preferred embodiment of the present invention, the downstream distribution of said conduit cross-section area is uniform.
Furthermore, in accordance with a preferred embodiment of the present invention, the downstream distribution of said conduit cross-section area is divergent.
Furthermore, in accordance with a preferred embodiment of the present invention, the downstream distribution of said conduit cross-section area is convergent.
Furthermore, in accordance with a preferred embodiment of the present invention, said fins are substantially perpendicular to said internal wall of the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, said fins are inclined with respect both to the general core-flow direction of motion and to the conduit internal walls.
Furthermore, in accordance with a preferred embodiment of the present invention, said fin typical thickness is of smaller order with comparison to the distance between two consecutive fins of same said fin array.
Furthermore, in accordance with a preferred embodiment of the present invention, said fin cross-section is substantially rectangular.
Furthermore, in accordance with a preferred embodiment of the present invention, said fin cross-section is substantially trapezoidal.
Furthermore, in accordance with a preferred embodiment of the present invention, said fin cross-section is substantially concave at least on one side.
Furthermore, in accordance with a preferred embodiment of the present invention, the distance between two consecutive fins is constant along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the distance between two consecutive fins varies along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the span of each of said fins is uniform along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the span of said fins varies along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the span of said fin is laterally uniform.
Furthermore, in accordance with a preferred embodiment of the present invention, the span of said fin laterally varies.
Furthermore, in accordance with a preferred embodiment of the present invention, the tips of said fins are sharp.
Furthermore, in accordance with a preferred embodiment of the present invention, the tips of said fins are blunt.
Furthermore, in accordance with a preferred embodiment of the present invention, the tips of said fins are curved.
Furthermore, in accordance with a preferred embodiment of the present invention, each of said fins substantially blocks half of the conduit lateral width.
Furthermore, in accordance with a preferred embodiment of the present invention, the two opposite fin arrays do not overlap.
Furthermore, in accordance with a preferred embodiment of the present invention, the two opposite fin arrays overlap.
Furthermore, in accordance with a preferred embodiment of the present invention, the ratio between the fin span and the gap between that fin and a consecutive fin of the same array of fins is in the range of 1:1 to 1:2.
Furthermore, in accordance with a preferred embodiment of the present invention, the ratio is about 1:1.5.
Furthermore, in accordance with a preferred embodiment of the present invention, the absolute value of the gap between the virtual plane connecting the fin tips of one of said two opposite fin arrays and the virtual plane connecting the fin tips of the second of said two opposite fin arrays is of smaller order than the lateral width of said conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, said absolute value of said gap is not more than 20% of the adjacent lateral width of said conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the size of each of said cavities is slightly smaller than the integrally defined natural scales associated with the vorticity of the vortex formed inside said cavity.
Furthermore, in accordance with a preferred embodiment of the present invention, is said conduit passive dimension defined as the dimension substantially parallel to said vortices virtual axes and substantially perpendicular to said core-flow motion is in the order of the fins span.
Furthermore, in accordance with a preferred embodiment of the present invention, said passive dimension is substantially larger than the other lateral dimension of the conduit that is substantially perpendicular to both the vortex axis and to the core-flow motion.
Furthermore, in accordance with a preferred embodiment of the present invention, said passive dimension follows a close substantially annular route.
Furthermore, in accordance with a preferred embodiment of the present invention, when Reynolds Number is increased inside said conduit further secondary vortices are formed.
Furthermore, in accordance with a preferred embodiment of the present invention, said core-flow downstream motion is substantially sinusoidal.
Furthermore, in accordance with a preferred embodiment of the present invention, the sinusoidal core-flow strongly interacts with the fins by local impingement of the core flow with the surfaces of the fins facing its motion.
Furthermore, in accordance with a preferred embodiment of the present invention when Reynolds Number is increased inside said conduit said core-flow breaks down locally and frequently generates unsteady secondary vortices intensively interacting with the core-flow or impinging on the surface of the facing fin.
Furthermore, in accordance with a preferred embodiment of the present invention, the vacuum within said vacuum reservoir is produced by a vacuum-pump.
Furthermore, in accordance with a preferred embodiment of the present invention, said vacuum reservoir is a vacuum-manifold.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduits are provided with an automated valve.
Furthermore, in accordance with a preferred embodiment of the present invention, the device is further provided with control and sensing means to serve the control task by actuating said valve by controlling the vacuum level or makes use of any other means of control.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduits are substantially parallel to said contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduits are conduits mount normally to said contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, said contact surface is a flat vacuum frame.
Furthermore, in accordance with a preferred embodiment of the present invention, said vacuum frame is rectangular.
Furthermore, in accordance with a preferred embodiment of the present invention, said vacuum frame is circular.
Furthermore, in accordance with a preferred embodiment of the present invention, said contact surface is cylindrical to present a drum-like contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, said contact surface includes grooves.
Furthermore, in accordance with a preferred embodiment of the present invention, the device used to convey an object with contact to said contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, it operates with respect to gravity.
Furthermore, in accordance with a preferred embodiment of the present invention, it operates irrespectful of the direction of gravity.
Furthermore, in accordance with a preferred embodiment of the present invention, it is provided a self-adaptive vacuum grip apparatus comprising: a vacuum source; a vacuum reservoir fluidically connected to said vacuum source; a contact surface; at least one conduit of a plurality of conduits; wherein said conduit has an inlet positioned on said contact surface and an outlet fluidically connected to said vacuum reservoir said conduit is provided with a helical fin mounted on the internal wall of said conduit thus a helical cavity is formed defined by said helical fin and said internal wall; wherein when a fluid flows through said conduit a helical vortex is formed within said helical cavity said helical vortex exists at least temporarily during said flow thus forming an aerodynamic blockage allowing a central core-flow between the vortex and the tip of said helical fin and suppressing the flow in a two-dimensional manner, thus limiting the mass flow rate and maintaining a substantial pressure drop within the conduit; whereby said core flow flows through a central passage defined by the helical fin internal edge and may locally bypass an obstruction in said central passage by following the helical passage adjacent the helical fin; and whereby when an object blocks the inlet of said conduit the flow stops said helical vortex dissipate thus said object is effectively held by the vacuum induced force to said contact surface whereas when the inlet is not blocked said vortices are formed and aerodynamically blocking the flow through said conduit and when said conduit is not blocked by said object the required vacuum level of said vacuum reservoir is maintained with significantly reduced power consumption supplied to generate the required vacuum condition.
Furthermore, in accordance with a preferred embodiment of the present invention, said fluid is air.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one barrier of a plurality of barriers is mounted substantially normally to said helical fin surface thus locally blocking the helical path to prevent the flow from following the helical path and thus said helical vortex locally splits by said barriers to at least two fragments.
Furthermore, in accordance with a preferred embodiment of the present invention, at least one barrier out of two barriers is mounted substantially normally to the fin surface on one of the two ends of said helical fin to act as anchorage for said helical vortex.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit follows a straight path.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit follows a tortuous path.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit cross-section is substantially circular.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit cross-section is substantially rectangular.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduit cross-section is substantially polygonal.
Furthermore, in accordance with a preferred embodiment of the present invention, the downstream distribution of said conduit cross-section area is uniform.
Furthermore, in accordance with a preferred embodiment of the present invention, the downstream distribution of said conduit cross-section area is divergent.
Furthermore, in accordance with a preferred embodiment of the present invention, the downstream distribution of said conduit cross-section area is convergent.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin is substantially perpendicular to said internal wall of the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin is inclined with respect both to the general core-flow direction of motion and the to conduit wall.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin thickness is of smaller order with comparison to said helical fin pitch.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin cross-section is substantially rectangular.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin cross-section is substantially trapezoidal.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin cross-section is substantially concave at least at one side having a fin root larger than the fin tip.
Furthermore, in accordance with a preferred embodiment of the present invention, the helical fin pitch is constant along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin pitch varies along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the span of said helical fin is uniform.
Furthermore, in accordance with a preferred embodiment of the present invention, the span of said helical fin varies along the conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the tip of said helical fin is sharp.
Furthermore, in accordance with a preferred embodiment of the present invention, the tip of said helical fin is blunt.
Furthermore, in accordance with a preferred embodiment of the present invention, the tip of said helical fin is curved.
Furthermore, in accordance with a preferred embodiment of the present invention, said helical fin span is substantially half of the conduit lateral width.
Furthermore, in accordance with a preferred embodiment of the present invention, the ratio between the helical fin span and the helical fin pitch is in the range of 1:1 to 1:2.
Furthermore, in accordance with a preferred embodiment of the present invention, the ratio is about 1:1.5.
Furthermore, in accordance with a preferred embodiment of the present invention, the central passage defined by the helical fin tip is of smaller order in comparison with the hydraulic diameter of said conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, said passage is not more than 30% of the adjacent lateral width of said conduit.
Furthermore, in accordance with a preferred embodiment of the present invention, the size of said helical cavity is slightly smaller than the integrally defined natural lateral scales associated with the vorticity of the helical vortex.
Furthermore, in accordance with a preferred embodiment of the present invention, when Reynolds Number is increased inside said conduit further secondary vortices are formed.
Furthermore, in accordance with a preferred embodiment of the present invention, the core-flow strongly interacts with said helical fin by local impingement with the surface of the helical fin facing its motion.
Furthermore, in accordance with a preferred embodiment of the present invention, when Reynolds Number is increased inside said conduit said core-flow breaks down locally and frequently generates unsteady secondary vortices, intensively interacting with the core-flow or impinging on the facing fin.
Furthermore, in accordance with a preferred embodiment of the present invention, the vacuum within said vacuum reservoir is produced by a vacuum-pump.
Furthermore, in accordance with a preferred embodiment of the present invention, said vacuum reservoir is a vacuum-manifold.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduits are provided with an automated valve.
Furthermore, in accordance with a preferred embodiment of the present invention, said device is further provided with control and sensing means to serve the control task by actuating said valve and controlling the vacuum level or makes use of any other means of control.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduits are fluidically connected to said contact surface wherein said conduits are parallel to said contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, said conduits are fluidically connected to said contact surface wherein said conduits mount normally to said contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, said contact surface is a flat vacuum frame.
Furthermore, in accordance with a preferred embodiment of the present invention, said vacuum frame is rectangular.
Furthermore, in accordance with a preferred embodiment of the present invention, said vacuum frame is circular.
Furthermore, in accordance with a preferred embodiment of the present invention, said contact surface is cylindrical to present a drum-like contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, said contact surface includes grooves.
Furthermore, in accordance with a preferred embodiment of the present invention, said device is used to convey an object with contact to said contact surface.
Furthermore, in accordance with a preferred embodiment of the present invention, it operates in the direction of gravity.
Finally, in accordance with a preferred embodiment of the present invention, it operates irrespectful of the direction of gravity.